The present invention relates generally to electronic solid state and integrated circuit devices. More specifically, the present invention relates to apparatuses for dissipating heat generated by such devices.
In the electronics and computer industries, it has been well known to employ various types of electronic device packages and integrated circuit chips, such as the PENTIUM central processing unit chip (CPU) manufactured by Intel Corporation and RAM (random access memory) chips. These integrated circuit chips have a pin grid array (PGA) package and are typically installed into a socket which is soldered to a computer circuit board. These integrated circuit devices, particularly the CPU microprocessor chips, generate a great deal of heat during operation which must be removed to prevent adverse effects on operation of the system into which the device is installed. For example, a PENTIUM microprocessor, containing millions of transistors, is highly susceptible to overheating which could destroy the microprocessor device itself or other components proximal to the microprocessor.
In addition to the PENTIUM microprocessor discussed above, there are many other types of semiconductor device packages which are commonly used in computer equipment, for example. Recently, various types of surface mount packages, such as BGA (ball grid array) and LGA (land grid array) type semiconductor packages have become increasingly popular as the semiconductor package of choice for computers. For example, many microprocessors manufactured by the Motorola Corporation, for use in Apple Corporation computers, employ BGA-type packages. Unlike a PENTIUM microprocessor with a PGA package, which has pins to be installed into a receiving socket, BGA and LGA semiconductor packages include an array of electrical contacts on their bottom surfaces to engage directly with an array of receiving electrical contacts on a circuit board, socket or the like. These semiconductor device packages have, in the past, been soldered directly to a circuit board or socket. However, such direct soldering makes replacement and/or upgrade of the semiconductor device package more difficult because it must be unsoldered from the board or socket for such replacement or upgrade.
To address the foregoing concerns, various sockets are being provided to receive, in temporary fashion, a BGA, LGA or similar surface mount semiconductor device package. In the event replacement or upgrade is required, the semiconductor package is simply removed from the socket and replaced with the new package. However, there are various concerns relating to the use of such BGA and LGA socket. For example, since no soldering is carried out in these new socket configurations, the solder balls of a BGA package and the contacts of an LGA must be maintained in electrical communication with the corresponding contact array on the socket. As a result, a minimum amount of pressure or force must be maintained on the semiconductor device package to maintain the electrical contact with the socket. It is not uncommon for the required minimum pressure to be in the vicinity of 50 psi (pounds per square inch) to maintain the electrical connection of the device package to the socket into which it is installed. If this pressure is not maintained, or is not consistent over the surface of the package, the electrical connection will fail.
Various efforts have been made to simply clamp the semiconductor device package, such as a BGA or LGA, to its corresponding socket by a top planar member with a series of screw fastening members sufficiently secured to attain the desired psi pressure on the package. However, BGA and LGA and similar packages commonly include a separate silicon portion containing the actual electronic components which is then subsequently mounted in some fashion to a larger ceramic base. Problems have arisen in connection with these BGA and LGA socket systems because at least 40 or 50 psi must be applied to the ceramic portion to maintain the socket interconnection; however, while the silicon pad region would be crushed and/or damaged by such a force applied thereto. It is not uncommon for such a device package to have a minimum 50 psi requirement on the ceramic portion to maintain the electrical interconnection to the socket while having a maximum 10 psi requirement on the silicon portion to avoid damage thereto.
In similar fashion to the PENTIUM-type semiconductor devices discussed above, the BGA, LGA and related device packages also suffer from excessive generation of heat. If such heat is not properly dissipated, the chip will eventually fail. As a result, efforts have been made to supply a heat dissipating member, such as a heat sink, into thermal communication with the silicon portion of the semiconductor device package, such as a BGA or LGA chip. As a result of the competing needs for heat dissipation and pressure to maintain the socket connection, problems arise. In particular, simple clamping of a heat sink member to the top portion of a BGA socket must be maintained at a pressure sufficient to maintain the electrical interconnections to the socket; however, such a high pressure creates a risk of damage to the silicon portion of the package.
The foregoing problems are exacerbated due to the different configurations of semiconductor packages which may be installed on a circuit board. For example, a BGA or LGA package may include a ceramic base with a sensitive silicon portion mounted directly on a central region thereon whereby the central portion of the resultant package of both silicon and ceramic is thicker than the outer ceramic only peripheral portion. Further, a semiconductor package may include a silicon portion which is embedded within the ceramic resulting in a flush top surface. Also, the ceramic portion of the package may have a recess in its upper surface for receiving the silicon member which results in the silicon member being recessed lower than the upper surface of the ceramic portion of the package. Still further, the silicon portion or portions of a semiconductor package may be carried about the periphery of the package in accordance with certain applications. In general, the aforementioned wide range of possible semiconductor package designs make the effective heat dissipation therefrom without damage to the package extremely difficult and cumbersome.
In view of the foregoing, there is a demand for a heat sink assembly which can simultaneously provide the requisite high pressure for maintaining a semiconductor device package in electrical interconnection with its corresponding socket while simultaneously providing a heat sink member in flush thermal communication with the silicon portion of a package at a second pressure much lower than the pressure being simultaneously applied to the ceramic portion of the semiconductor device package. In addition, there is a demand for a heat sink assembly that can independently adjust the pressure applied to the ceramic portion of a package while permitting custom adjustment of the pressure of a heat sink applied to the silicon portion of the same semiconductor device package.